Tin-plated copper-alloy material for terminal is formed by reflowing after Cu-plating and Sn-plating on a substrate made of copper alloy so as to have a Sn-based surface layer as a surface layer and a Cu—Sn alloy layer as a lower layer, and is widely used as material for terminal.
In recent years, for example, electrification is rapidly progressed in vehicle and circuits are increased in the electrical equipment, so that connector used in the circuit is remarkably downsized and the pins thereof are increased. When the connector have a lot of pins, even though a force for inserting the connector for a pin is small, a large force is required for inserting the connector for all pins; therefore, it is apprehended that productivity is deteriorated. Accordingly, it is attempted to reduce the force for inserting for a pin by reducing the friction coefficient of tin-plated copper-alloy material.
For example, it is described that a surface-exposure rate of the Cu—Sn alloy layer is defined by roughing the substrate (in Patent Document 1). However, there are problems of increasing contact resistance or deteriorating soldering wettability. Also, it is described that average of roughness of the Cu—Sn alloy layer is defined (in Patent Document 2). However, for example, there is a problem in which a dynamic friction coefficient cannot be reduced to 0.3 or less for furthermore improving insertion/extraction performance.